ENGR 12 Engineering Circuits

1. ENGR 12Engineering Circuits Tom Rebold

2. Lecture 1A: Basic Concepts

3. Today • Why this stuff matters • What is voltage and current • physics vs common sense • Ideal Circuit Element • And some real ones: Resistors, Capacitors, Inductors • Power and Energy • Voltage and Current Sources

4. Later This Week… • Ohms Law • Network Topology • Kirchoff’s Circuit Laws

5. Circuit Theory is a Pre-requisite for • Analog and digital circuits • Amplifiers, Power System, Integrated Circuits • Communication systems design • Filters, Modulation theory, Signal Processing • Computer architectures • Control of electro-mechanical systems • Feedback, stability analysis

6. Solid State • Devices • Transistors • Diodes (LED’s, Laser diodes) • Photodetectors • Miniaturization of electrical devices • Integration of many devices on a single chip

7. Digital Logic • Based on logic gates, truth tables, and combinational and sequential logic circuit design • Uses Boolean algebra and Karnaugh maps to develop minimized logic circuits.

8. Power Systems • Generation of electrical energy • Storage of electrical energy • Distribution of electrical energy • Rotating machinery-generators, motors

9. Communications/Signal Processing • Transmission of information electrically and optically • Modification of signals • enhancement • compression • noise reduction • filtering

10. Controls • Changing system inputs to obtain desired outputs • Feedback • Stability

11. Introduction to Electric Circuits • Here we are going to remind what are: • Voltage • Current • Current flow • Voltage Sources • Voltmeter (Multimeter)

12. H2O Low Pressure High Pressure What is Voltage? V = “Electrical pressure” - measured involts. Figure 1.1

13. A battery in an electrical circuit plays the same role as a pump in a water system.

14. Lab Power Supply Solar Cell Electric Power Plant A Battery Nerve Cell What Produces Voltage? V = “Electrical pressure” 9 V 1.5 V A few Volts A few millivoltswhen activated bya synapse 13,500 V

15. + + ~ _ _ Battery Time-varyingsource Solar Cell Generator (power plant) . Other Symbols Used for Specific Voltage Sources These are all… Voltage Sources Figure 1.2

16. This supply goes upto 10 V The voltage is adjustable via this knob Lab Power Supply The red (+) and black (-) terminals emulate the two ends of a battery. Remember: A voltage is measured between two points A Typical Voltage Source The white terminal is connected to earth groundvia the third prong of the power cord

17. volts • Connect COM (common) • of the meter to power supplyblack I COM V Measuring Voltages We can measure voltage between two points with a meter • Set the meter to read • Voltage +2.62 • Connect the V of the • meter to power supply red • Read the Voltage white

18. –3.2 V Answer: –3.2 V I COM V Exercise The power supply is changed to 3.2 V. What does the meter read? What’s the answer? Find out

19. + + + V1 V2 V3 _ _ _ Point of Reference What is “Ground” “Ground” refers to the reference terminal to which all other voltages are measured Figure 1.3

20. + V2 _ The earth is really just one big ground node. Most people choose the earth as the reference ground when a connection to it is available. A ground connection to earth is often made via the third prong of a power cord.

21. Ground Symbol Positive relative to ground + + + V1 V2 V3 _ _ _ + _ Negative relative to ground V4 Figure 1.4

22. Voltage Relative to Ground The white terminal is connected to earth ground Connect the black terminal to ground The red terminal is positive with respect to “ground” +

23. Negative Polarity Relative to Ground The black terminal is negative with respect to ground. +

24. What is Current? • Current is the flow of charge from a voltage source • 1 Ampere (“Amp”) = Flow of 1 Coulomb/sec +++

25. Metal wires (conductors) How Does Current Flow? Current can only flow through conductors +++ Currentflow

26. Plastic material (insulators) When Does Current NOT Flow? Current cannot flow through insulators +++ No currentflow

27. +++ Note that Air is an Insulator Current cannot flow through insulators Air No current flow That’s why a battery doesn’t discharge if left on its own.

28. What is Current? • Electricity flows when electrons travel through a conductor. • We call this flow “current.” • Only some materials have free electrons inside. glass rubber oil asphalt fiberglass porcelain ceramic quartz (dry) cotton (dry) paper (dry) wood plastic air diamond pure water YES! silver copper gold aluminium iron steel brass bronze mercury graphite dirty water concrete Conductors: NO! Insulators: No free electrons = No current

29. Current • Current is the amount of electric charge (coulombs) flowing past a specific point in a conductor over an interval of one second.  1 ampere = 1 coulomb/second • Electron flow is from a lower potential (voltage) to a higher potential (voltage).

30. Current • For historical reasons, current is conventionally thought to flow from the positive to the negative potential in a circuit.

31. Formal Definition of Current Flow • Rate of flow of “positive” charge • Measured in Coulombs per second of charge • (It’s really the electrons flowing in the opposite direction) 1 Ampere = 1 Coulomb of electrons flowing by per second in the wire

32. - - - - - - - - - - - - - - - - - - - - - - - - electron motion positive current direction Sign Convention for Current Flow • Electrons carry negative charge • Positive current flow is in opposite direction

33. Textbook Definitions • Charge: bipolar (+/-), basic unit 1.6e-19 C • Effects from separation (volt) and flow (current) • Voltage: the energy needed to separate +/-charges by a certain distance • Not unlike the energy needed to lift an object in a gravity field • V = dw/dq = delta energy / delta charge • W is in Joules, q is in coulombs • Unit: 1 V = 1 Joule/ Coulomb

34. Current: rate of flow of electrical charges • I = dq/dt = delta charge /delta time • q is in Coulombs, t in seconds • Unit: 1 Amp is a flow of 1 Coulomb / sec

35. i + v - 1 2 The Ideal Circuit Element • Could be battery, resistor, capacitor, etc. • Defined by a mathematical model • Polarity is arbitrary • We choose the “passive sign convention” • Voltage “drop” from terminal 1 to 2 • Positive charge flowing from term 1 to 2

37. Power and Energy • Often more useful quantities in understanding a circuit • How many kilowatt-hours did you use last month? • Many circuits have power limits • Beyond which, you “fry” the circuit! • Power is the time rate of expending or absorbing energy • p = dw/dt • Unit: 1 W = 1Joule / second

38. i + V “Passive” sign convention i + + _ V Power Flow The current variable i is defined as positive into the (+) terminal of the element If the physical current is positive Power flows into the element) P = V i The current variable i is defined as positive into the (+) terminal of the element Here the physical current is negative Power flows out of the source P = V i

40. Voltage and Current Sources • Ideal Voltage Source • Maintains voltage regardless of current • Ideal Current Source • Maintains current regardless of voltage + - vs is

41. Dependent (Controlled) Sources • Controlled by a voltage or current elsewhere in the circuit • Voltage controlled voltage source • Voltage controlled current source • Current controlled voltage source • Current controlled current source vs =kvx + -

42. Example 1.1 • Which interconections are valid/invalid?

43. Example 1.2 p 13 valid/invalid?? • Which interconections are valid/invalid?

44. i + v - 1 2 Summary • Circuits are foundational for many of the most exciting engineering topics • Voltage is like water pressure, current is like water flow • “Ideal Element” follows “Passive Sign Convention” • Ideal Sources can provide constant voltage or current, or can depend on some other part of circuit